diff --git a/mediafile.py b/mediafile.py
index 4ac373a..2256b63 100644
--- a/mediafile.py
+++ b/mediafile.py
@@ -1843,6 +1843,14 @@ def update(self, dict):
         StorageStyle('MUSICBRAINZ_ALBUMCOMMENT'),
         ASFStorageStyle('MusicBrainz/Album Comment'),
     )
+    releasegroupdisambig = MediaField(
+        # This tag mapping was invented for beets (not used by Picard, etc).
+        MP3DescStorageStyle(u'MusicBrainz Release Group Comment'),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz '
+                        'Release Group Comment'),
+        StorageStyle('MUSICBRAINZ_RELEASEGROUPCOMMENT'),
+        ASFStorageStyle('MusicBrainz/Release Group Comment'),
+    )
 
     # Release date.
     date = DateField(
diff --git a/test/test_mediafile.py b/test/test_mediafile.py
index 8d1ea8b..887d23d 100644
--- a/test/test_mediafile.py
+++ b/test/test_mediafile.py
@@ -395,6 +395,7 @@ class ReadWriteTestBase(ArtTestMixin, GenreListTestMixin,
         'albumstatus',
         'media',
         'albumdisambig',
+        'releasegroupdisambig',
         'artist_credit',
         'albumartist_credit',
         'original_year',